Due to the inverse square law of illumination, the intensity of light falling on a target area decreases in proportion with the square of the distance. When using a camera and lens arrangement to view a typical surveillance scene a certain proportion of the image contains the foreground and a certain amount the background. The amount of light required or optimal to illuminate the foreground of a target area is usually much lower than that required to illuminate the background of a target area. Additionally target areas in surveillance are typically more extended horizontally than vertically, because most target areas are based on a horizontal ground area, across which peoples or vehicles travel.
Most illumination systems produce a circularly diverging beam which when used with a camera, which requires the installer to point the peak of the beam at the farthest target point. For a fixed target distance there is an optimum beam profile in the vertical orientation. When viewing at the same distance with a wider and wider view and matching the circular illumination the illuminator moves further away from the optimum in the vertical orientation and wastes more light. Moreover, as the peak of the light source is pointed above the line of the target, a large proportion of the light is above the target area and is not utilized.
There are many systems which use infrared illumination for low light photography or video photography. There are also many systems which use LEDs for photographic or video illumination. Some of these systems utilize refractive or reflective elements to diffuse or focus illumination.
Illuminators using LEDs with refractive or reflective elements to enhance illumination are varied and include a number of different types of refractors which channel light from the LEDs so as to alter the distribution of illumination on the target and/or to make illumination more efficient by conserving light.
There are also a number of devices in which lights are fitted with micro-prisms or similar constructions to refract light onto a target. Some of these devices are used in projectors or similar systems or in media effects systems for backlighting.
Several necessities prior to this invention have combined to limit the technology of low light illumination for wide-angle nighttime surveillance video photography, particularly for license plate capture and reading, when several vehicles' headlights may be pointed toward a surveillance camera. There is a need to pulse the surveillance illumination to conserve energy. There is a need to synchronize a surveillance camera to the pulsed illumination returning to the camera after having fallen on a moving target. There is a need to illuminate a wide area in the case of vehicles traveling across lanes or where multiple lanes of vehicles are targeted. There is a need for wide-angle effective illumination matching wide-angle high pixel density cameras in order to capture tiny fast-moving license plates out of a large wide-angle scene such as a multi-lane freeway.